What is an explorable explanation?

It's our way-too-long phrase for a thing that explains an idea through play.
You can say "explorable" for short.
Here's some examples of explorables made in 3 weeks or less,
to give you an idea of what you can make during
#ExplorablesJam!

How can I make an explorable?

And if you need to host your explorable somewhere on the internet for free,
github pages
or
itch.io
are good bets.

Who else is making explorables?

You can come hang out on the
r/Explorables subreddit
during the jam! (or for that matter, before and after the jam)
Show off what you're working on, give & get feedback, discuss ideas,
do... whatever it is a "community" does?